The use of xe2x80x9cin-situxe2x80x9d carbon dioxide generation, to deliver fluids is described in U.S. Pat. No. 5,398,851. In this instance, carbon dioxide is produced by chemical reaction of a sodium carbonate with an aqueous citric acid solution. These fluid delivery devices are rather inaccurate, mainly due to the difficulty to achieve and maintain a constant gas generation rate. Furthermore, their use is limited, since gas generation can not be controlled, varied or stopped.
Improvements over such devices are described in the Maget U.S. Pat. No. 5,971,722. In this instance the gas generator is electrochemically controlled and thereby achieves higher accuracy levels, without adding complexities or cost.
Commercial carbon dioxide gas generation systems, such as Becton-Dickinson""s GasPak (tm), which are used in microbiology, are also based on the chemical reaction between sodium bicarbonate and citric acid.
In all instances, when carbon dioxide is generated by chemically reacting a metal (bi)carbonate with an acid, the reaction, once started is difficult to control, can not be conveniently stopped and at reaction completion residues containing chemicals, binders and additives are present, dissolved or in suspension in solution.
Hydrogen-driven fluid delivery is exemplified by the Disetronic Infuser disposable syringe pump, which uses a galvanic cell as a hydrogen source.
Commercial hydrogen gas generation systems, such as GasPak used in microbiology, are based on the chemical reaction of sodium borohydride with citric acid.
Again, these hydrogen generators are difficult to stop or to control to achieve a constant pre-set gas generation rate.
The present invention, based on selecting CO2 and H2 containing organic compounds, and an electrochemical decomposition process, results in the controlled generation of CO2 and H2, the rate being variable at will, which includes stops and restarts, and without formation of by-products.
The electrochemical cell, suitable for the practice of the present invention, is described in the Maget U.S. Pat. No. 6,010,317 and is hereby included by reference.
The organic acids suitable as sources of carbon dioxide, are of the family of mono- and polycarboxylated hydrocarbons, exemplified by formic acid, oxalic acid, tricarballylic acid, succinic acid, and the likes.
By applying energy, provided from an external d.c. power source, an anodic process strips hydrogen from the organic acid, releases hydrogen which is ionized and transported to the counterelectrode, while releasing carbon dioxide as the anodic product. In the instances when the organic acid only contains hydrogen and carbon dioxide, such as formic acid and oxalic acid, the anodic gas released during the process is mainly carbon dioxide, and the cathodic gas is mainly hydrogen. In this manner the CO2 and H2 generation rates are controlled by the applied current, and can thus be readily started, stopped or regulated.
It is the primary object of this invention to provide for a carbon dioxide generator which can be controllably operated.
It is another object of this invention to provide for a small, compact, self-contained, battery operated carbon dioxide generation apparatus.
It is the third object of this invention to provide carbon dioxide on demand, at a rate predictable from an applied current.
It is the fourth object of this invention to generate a high purity carbon dioxide.
It is a fifth object OF this invention to generate carbon dioxide without production of insoluble reaction by products.
The sixth to the tenth objects of this invention are similar to objects one to five, except that they are related to the generation of hydrogen.
These and other objects of the instant invention will become more apparent from the claims, specification, drawings and experiments.